In the field of producing printed wiring boards, photosensitive resin compositions have been widely employed as resist materials used for etching or plating. The photosensitive resin composition is often used as a photosensitive element (layered product) provided with a support and a layer which is formed on the support using the photosensitive resin composition (hereinafter, sometimes referred to as “photosensitive resin composition layer”).
For example, the printed wiring board is manufactured as follows. First, a photosensitive resin composition layer is formed on a substrate for forming circuits using a photosensitive element (photosensitive layer forming process). Next, the predetermined area of the photosensitive resin composition layer is irradiated with active light rays to cure the exposed area (exposure process). Then, a support is peeled, and the unexposed area of the photosensitive resin composition layer is then removed (developed) from the substrate, thereby forming a resist pattern, which is the cured material of the photosensitive resin material (hereinafter, sometimes referred to as “resist cured product”), on the substrate for forming circuits (developing process). The resist pattern obtained is used for etching or plating to form a circuit on the substrate (circuit forming process), and finally the resist pattern is released and removed (releasing process) to produce a printed wiring board.
As an method of exposure, a method in which exposure is carried out through a photomask using a mercury lamp as a light source is conventionally employed. Recently, an method of exposure called DLP (Digital Light Processing) or LDI (Laser Direct Imaging) has been proposed as a direct writing exposure method that allows direct formation of patterns. Such a direct writing method of exposure has improved alignment accuracy than the method of exposure through a photomask and allows the formation of finer patterns, and therefore increasingly used to manufacture substrates for high density package substrates.
In general, in the exposure process, the exposure time is desired to be reduced in order to improve the production efficiency. In the above-described direct writing method of exposure, however, monochromatic light such as laser is used as a light source and the substrate is irradiated with light rays while scanning. Therefore, the direct writing method of exposure tends to require a longer exposure time as compared to the conventional method of exposure carried out through a photomask. Accordingly, in order to reduce the exposure time to improve the production efficiency, it is necessary to improve the sensitivity of the photosensitive resin composition than the conventional one.
Meanwhile, in association with recent increase in density of printed wiring boards, the demand for a photosensitive resin composition that allows the formation of a resist pattern with sufficient resolution (resolution property) and adhesiveness is increasing. In particular, it is difficult to form a resist pattern having a L/S (line width/space width) of 10/10 (unit: μm) or less in manufacture of a package substrate.
Regarding these demands, various photosensitive resin compositions have been examined in the past. For example, a photosensitive resin composition in which the above required features are improved by using a styryl pyridine as a sensitizing dye is proposed in, for example, Chinese Patent Publication No. 101738861. Further, a photosensitive resin composition in which the above required features are improved by using a specific binder polymer, a photopolymerizable compound, a photopolymerization initiator, and a sensitizing dye is proposed in Japanese Patent Application Laid-Open (JP-A) Nos. 2006-234995 and 2007-114452, and International Publications Nos. WO 08/078483, WO 10/098175 and WO 10/098183.